This invention relates to a radio receiver, such as a super heterodyne receiver, for receiving a radio signal.
A conventional radio receiver includes a receiving section for receiving the radio signal and for producing a received signal. In the manner known in the art, the radio signal carries one or more baseband signals. A reference oscillator is for producing a reference signal having a reference frequency. An oscillation producing section is connected to the reference oscillator for producing a local signal according to the reference signal. In other words, the local signal is related to the reference signal as regards their frequencies. A mixing section is connected to the receiving section and the oscillation producing section for mixing the received signal with the local signal to produce an IF signal having an intermediate frequency. A demodulator demodulates the IF signal into the baseband signal or signals.
The radio receiver may be a double super heterodyne receiver. In this event, the oscillation producing section comprises first and second local oscillators. The first local oscillator produces a first local signal which is related to the reference signal as regards their frequencies. The second local oscillator produces a second local signal which is not related to the reference signal in frequency. The mixing section comprises first and second mixing units. The first mixing unit is connected to the receiving section and the first local oscillator for mixing the received signal with the first local signal to produce a first IF signal. The second mixing unit is connected to the first mixing unit and the second local oscillator for mixing the first IF signal with the second local signal to produce a second IF signal having an eventual frequency which corresponds to the above-mentioned intermediate frequency.
As will later be described more in detail, the conventional radio receiver is defective in that the intermediate frequency or the eventual frequency has a frequency drift.